420 



ODce and specifically to a particular fault in diet, to an injudicious use 

 of cold water when the system is heated, to a fault in drainage, venti- 

 lation or lighting of the stables, to indigestion, to liver disease, to 

 urinary disorder, etc. 



STRUCTURE OF THE SKIN. 



The skin consists primarily of two parts: (1), the superficial nonvas- 

 cular (without blood vessels) layer, the cuticle or epidermis; and (2), the 

 deep vascular (with blood vessels) layer, the corium, dermis or true skin. 



The cuticle is made up of cells placed side by side and more or less 

 modified in shape by their mutual compression and by surface evapora- 

 tion and drying. The superficial stratum consists of the cells dried in 

 the form of scales, which fall ofl" continually and form dandruff. The 

 deep stratum (the mucous layer) is formed of somewhat rounded cells 

 with large central nuclei, and in colored skin containing numerous pig- 

 ment granules. These cells have prolongations. or branches by which 

 they communicate with each other and with the superficial layer of 

 cells in the true skin beneath. Through these they receive nutrient 

 liquidsfortheirgrowth and increase, and through these liquids absorbed 

 by the skin, may be passed on into the vessels of the true skin beneath. 

 The living matter in the cells exercises an equally selective power oa 

 what they shall take up for their own nourishment and on what they 

 shall admit into the circulation from without. Thus, certain agents 

 like iodine and belladonna are readily admitted, whereas others, like 

 arsenic, are excluded by the sound unbroken epidermis. Between the 

 deep and superficial layers of the epidermis there is a thin translucent 

 layer (septum lucidum), consisting of a double stratum of cells, and 

 forming a medium of transition from the deep spheroidal to the super- 

 ficial scaly cuticle. 



The true sl-in or dermis has a framework of interlacing bundles of 

 ■white and yellow fibers, large and coarse in the deeper layers, and fine 

 in the superficial where they approach the cuticle. Between the fibrous 

 bundles are left interspaces which, like the bundles, become finer as 

 they approach the surface, and inclose cells, vessels, nerves, glands, 

 gland ducts, hairs, and in the deeper layers fat. 



The superficial layer of the dermis is formed into a series of minute 

 conical elevations or pajnlla, projecting into the deep portion of the 

 cuticle, from which they are separated by a very fine transparent mem- 

 brane. This papillary layer is very richly supplied with capillary blood 

 vessels and nerves, and is at once the seat of acute sensation and the 

 point from which the nutrient liqurd is supplied to the cells of the 

 cuticle above. It is also at this point that the active changes of in- 

 flammation are especially concentrated; it is the immediately super- 

 posed cell layers (mucous), that become morbidly increased in the early 

 stages of inflammation ; it is on the surface of the papillary layer that 

 the liquid is thrown out which raises the cuticle in the form of a blister, 

 and it is at this point mainly that pus forms in the ordinary pustule. 



